Method of feeding glass batch to a glass-melting furnace

ABSTRACT

A method of feeding glass to a glass-melting furnace for making a vitreous material, a heated airstream containing air at a temperature in excess of 1,000° C. is passed down vertical cylinders towards the crown of the glass-melting furnace. Powdered glass batch is introduced into the vertically moving heated airstream in the lower and wider cylinder and infra-sound is applied to the vertically moving heated airstream by an infra-sound generator to vibrate the heated airstream and effect heat transfer from the airstream to the glass batch particles so that the glass batch particles are heated and the temperature of the heated airstream is reduced to a temperature below 700° C., thereby reducing the propensity of the air to produce nitrogen oxides. Fuel is subsequently added as the heated glass batch particles and the cooled airstream move downwardly towards the crown of the furnace and a stream of glass batch, burning fuel and air is passed downwardly through the crown of the furnace in a manner such that there is a direct contact between the flame of the burning fuel and the surface of molten glass within the furnace, and the glass batch is melted.

FIELD OF THE INVENTION

This invention relates to a method of feeding glass batch to aglass-melting furnace.

SUMMARY OF THE INVENTION

In accordance with the present invention a method of feeding glass batchto a glass-melting furnace includes the step of feeding powdered glassbatch vertically downwardly through a hot air environment, applyinginfra-sound to the hot air environment containing the powdered glassbatch to facilitate transfer of heat from the hot air environment to thepowdered glass batch and, subsequent to the said heat transfer, addingfuel to the heated glass batch to raise the temperature of the glassbatch to melting temperature.

The application of the infra-sound facilitates transfer of heat from thehot air environment to the powdered glass batch by imposing avibrational relative movement between the hot air and the powdered glassbatch.

Preferably in accordance with the present invention the heat transferfrom the hot air environment to the glass batch cools the hot airenvironment to a temperature of the order of 700° C. or even to atemperature lower than 700° C.

Such cooling of the hot air environment is important in substantiallyreducing the propensity of the airstream to produce nitrogen oxides(NO_(x)) when the airstream reacts with fuel immediately upon thecombustion resulting from the introduction of the fuel.

The hot air environment is advantageously provided by an airstream whichis pre-heated by waste gases from the glass-melting furnace. Theairstream is preferably pre-heated to a temperature of the order of1,200° C.

Such pre-heating may be effected in stages by passing air from theatmosphere through successive heat exchangers.

More specifically in accordance with the present invention, there isprovided a method of feeding glass batch to a glass-melting furnace formaking a vitreous material comprising the steps of passing a heatedairstream containing air at a temperature in excess of 1,000° C.vertically downwardly towards the crown of the glass-melting furnace,introducing powdered glass batch into the vertically moving heatedairstream, applying infra-sound to the vertically moving heatedairstream to vibrate the heated airstream and effect heat transfer fromthe airstream to the glass batch particles to heat the glass batchparticles and reduce the temperature of the heated airstream below 700°C., subsequently adding fuel as the heated glass batch particles and thecooled airstream move downwardly towards the crown of the furnace, andpassing a stream of glass batch, burning fuel and air downwardly throughthe crown of the furnace such that there is direct contact between theflame of the burning fuel and the surface of molten glass within thefurnace, and the glass batch is melted.

In the embodiment of the invention which will be described, the fuel isadded around a circumference of the downwardly moving airstream andheated glass batch particles, but the fuel may be injected into thedownwardly moving airstream and heated glass batch particles.

By the use of the present invention it has proved possible to formglasses having high melting points, for example a melting point inexcess of 1400° C., which have proved difficult to produce inconventional furnaces.

The present invention will be further understood from the followingdetailed description of preferred embodiments thereof which is made, byway of example, with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are respectively elevation and plan views of apparatusincluding a furnace for carrying out the method of present invention,

FIG. 2 is a graph showing the relationship between the production ofnitrogen oxides (NO_(x)) upon gaseous combustion in pre-heated air andthe temperature of the pre-heated air when the fuel is introduced andcombustion is commenced, and

FIG. 3 is a diagrammatic representation of an alternative apparatus forcarrying out the method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1a and 1b of the accompanying drawings, there isshown a glass-making furnace 1 having a crown 2 and containing moltenglass 3. The crown 2 of the furnace 1 supports a cylinder 4 throughwhich heated glass batch and flame are fed into the interior of thefurnace.

Waste gases from the furnace 1 exit through a vertical duct 5 and aredrawn through upper part of heat exchanger 6, ducting 17, upper part ofheat exchanger 7 and further ducting 18 by a fan 19 to the base of achimney stack 8 through which the waste gases are vented to atmosphereafter suitable filtration.

The heat exchangers 6 and 7 each comprise a moving pebble bedregenerator based on the pebble bed heater described by C. L. Norton Jr.in the Journal of The American Ceramic Society, Volume 29, (1946) No. 7,pages 187-193. The pebble bed regenerators 6 and 7 may be additionallyused to remove oxides of nitrogen (NO_(x)) and oxides of sulphur(SO_(x)) by addition of ammoniacal water and alkali respectively, asdescribed in my co-pending International Patent Application No. PCT/GB89/01361.

However, by use of the preferred method in accordance with the presentinvention, the quantities of NO_(x) produced on combustion may be sosmall that a special treatment with ammoniacal water to remove NO_(x)from the waste gases may not be required.

Air from ambient atmosphere is drawn by a fan 9 through a lower part ofpebble bed regenerator 7 and thereafter through a lower part of pebblebed regenerator 6 so that the air acquires heat in the pebble bedregenerators 7 and 6. The air is heated during its passage through thepebble bed regenerators 7 and 6 by taking heat from the heated pebblesmoving under gravity in those pebble bed regenerators so that the air isheated to a temperature of the order of 1200° C. The heated air is thenfed through ducts 10 and 11 and down a vertical cylinder 12, which isconcentric with cylinder 4 above the crown of furnace 1.

An infra-sound generator 13 generates sound waves at a frequency of15-20 cycles per second at a level of the order of 140 decibels, andthese sound waves are passed directly down the cylinder 12, through awider cylinder 20, and further through cylinder 4 into the interior ofthe furnace 1 where the sound waves are reflected from the surface ofthe molten glass 3.

A glass batch in powder form is fed from a hopper 14 through a channel15 into the heated air in the wider cylinder 20. The particles of glassbatch so introduced are in suspension in the heated air which is beingvibrated in the wider cylinder 20 by the action of the infra-sound. Theinfra-sound causes a vibrational relative movement between the heatedair and the particles of powdered glass batch. An enhanced heat transferbetween the hot airstream and the powdered glass batch is thus effectedand the temperature of the heated air is reduced to a temperature in therange of 500° C. to 600° C.

Accordingly much of the waste heat recovered from the glass-meltingfurnace is transferred to the glass batch before any fuel is added. Thelowering of the temperature of the heated air as a result of this heattransfer results in a lowering of the temperature of the furnace wastegases and therefore a lowering of the propensity of the air to produceNO_(x) as will be discussed later in relation to FIG. 2 of theaccompanying drawings.

The partially heated glass batch passes downwardly from cylinder 20 tocylinder 4, into which fuel, for example gas or oil, is injectedvertically downwardly through vertical inlets in a part 16, whichsurrounds the lower end of cylinder 20 and enables fuel to be injectedto mix with the air and glass batch passing through cylinder 4 where thefuel ignites. As the glass batch passes down through cylinder 4, theburning fuel in cylinder 4 raises the temperature of the glass batchsubstantially to the melting temperature of the components of the glassbatch and the flame and heated batch both contact the surface of moltenglass 3 in the furnace 1. The direct flame contact upon thinlydistributed batch on the hot molten surface in the furnace 1 encouragesmelting and maturing of the batch into hot molten glass.

In operation of a furnace as described above, in which the batch was amixture of flyash and limestone which was difficult to melt, an outputof 24 tonnes per day of glass was obtained from a batch area of 7 m² inthe furnace, when the furnace was operating on cold air and the meltingpoint of the glass was 1440° C. The constitution of the final glass was

45% CaO

30% SiO₂

15% Al₂ O₃

the balance being Fe₂ O₃, TiO₂, a little alkali etc.

Reference is now made to FIG. 2 of the accompanying drawings, which is agraph showing the relationship between the production of nitrogen oxides(NO_(x)) upon gaseous combustion in pre-heated air and the temperatureof the pre-heated air when the fuel is introduced and combustion iscommenced.

The graph of FIG. 2 shows that the rate of NO_(x) production in thepresence of fossil fuels, gas or oil is low when the preheat temperatureof the air is below 700° C. Above 700° C. the rate of NO_(x) productionincreases very significantly and from 800° C. upwards the rate of NO_(x)production escalates at a rapid rate.

Typically on conventional furnaces, fuel is introduced into airpre-heated to a temperature in a range of about 1000°-1100° C. asindicated by arrows C, D in FIG. 2, which results in the production ofNO_(x) to an extent of about 2000 ppm of NO_(x) per cubic foot of wastegas.

However, by the use of the method according to the present invention asdescribed with reference to FIGS. 1a and 1b, the pre-heat temperature ofthe air is reduced to be within the range of 500°-600° C. as indicatedby arrows E and F in FIG. 2, and the amount of NO_(x) produced is onlyof the order of 300 ppm of NO_(x) per cubic foot of waste gas.

In FIG. 3 of the accompanying drawings there is shown diagrammaticallyan alternative apparatus for carrying out the method of the presentinvention using static bed heat regenerators for preheating the air.

Referring to FIG. 3 there is shown a glass melting furnace 25 having areaction tower 26 through which the furnace 25 is vertically fired andfed. Tower 26 has upper and lower co-axial cylindrical sections and aninfrasound generator 29 mounted to direct infrasound waves down thetower 26. Preferaby the sound waves have a frequency of 15 to 20 cyclesper second and an energy level of 140 decibels. The infrasound waves aredirected vertically down the tower 26 and reflected from the surface ofmolten glass 30 in the furnace 25, to impart vertical vibrations to thegas in the tower 26.

Powdered glass batch is fed intermittently and substantially axiallyinto the top of the tower 26 as shown at 31. Heated air is alsointroduced substantially at the top of the upper section 27 of the tower26 as shown at 32.

The heated air introduced at 32 is at a temperature of the order of1200° C. and by virtue of the infrasound waves the molecules of theheated gas will be vibrated in the upper cylindrical section 27 of thetower 26 so that a good heat transfer from the hot air to the powderedglass batch introduced at 31 occurs in the upper cylindrical section 27of the tower 26. The temperature of the hot air is reduced to atemperature in the range 500° to 600° C. by the time the pre-heatedglass batch reaches the junction between the upper and lower cylindricalsections 27 and 28 immediately below which the fuel, which may be oil orgas, is introduced into the wider lower cylindrical section 28 of thetower 26. The resulting combustion in the lower cylindrical section 28raises the temperature of the glass batch substantially to the meltingtemperatures of the components of the batch and the heated glass batchdrops fall on the surface of the molten glass 30. The flame from thecombustion in the lower cylindrical section 28 also impinges on thesurface of the molten glass 30 and fans out over the surface of themolten glass 30 ensuring full melting of the glass batch components andmaturing of the glass of the desired composition which is recovered fromthe furnace through feeder tube 33.

In the apparatus of FIG. 3 the hot air is ambient air heated by wastegases from the furnace using static regenerator beds 34 and 35. Wastegases are taken from the furnace 25 as shown at 36 and fed alternativelyto static bed regenerator 34 or static bed regenerator 35 according tothe position of valves V1 and V2. In the position illustrated in FIG. 3valve V1 is closed and valve V2 is open, so that the waste gases canpass to the top of regenerator bed 35 but cannot enter regenerator bed34.

Fan 37 is therefore able to draw the hot waste gases through open valveV2, regenerator bed 35 and open valve V6, after which the waste gasesare passed to a chimney (not shown) for discharge into the atmosphereafter suitable filtration. Regenerator bed 35 is thus in the waste gasreceiving part of its cycle, whereas regenerator bed 34, as will now bedescribed, is in the air delivery part of its cycle.

Air from the atmosphere is drawn under the influence of a fan 38 throughducts to feed either valve V7 or valve V8. In the operating position ofthe apparatus shown in FIG. 3, where waste gases are heating regeneratorbed 35, valve V8 is closed and air drawn from the atmosphere by fan 38passes through open valve V7 into the base of regenerator bed 34 whichwas heated by furnace waste gases in the immediately preceding waste gasreceiving part of its cycle. The air passes through regenerator bed 34and is removed from the upper part of that bed 34 through open valve V3and fed to the top of the upper cylindrical section 27 of the reactiontower 26 at 32 as previously described.

The positions of all of the valves V1 to V8 are reversed from the closedto the open or the open to the closed position at regular intervals ofbetween 15 seconds and 3 minutes depending on the size of theregenerator beds 34 and 35, in order to maintain both regenerator beds34 and 35 at maximum temperature.

When a reversal of the regenerator system is to be made the operatingconditions of the valves are changed in the following order.

First, valves V2 and V6 are closed and valves V8 and V4 are opened.These valve changes stop the introduction of waste gases intoregenerator bed 35 and allow atmospheric air drawn into the system byfan 38 to be passed through valve V8, heated regenerator bed 35 andvalve V4 to the line or ducting 32 and the upper end of uppercylindrical section 27 of the reaction tower 26. At this instant heatedgas is being supplied to the upper cylindrical section 27 of thereaction tower 26 through both regenerator beds 34 and 35.

Once the flow of heated air to the reaction tower 26 through regeneratorbed 35 has been established, the operating conditions of valves V3, V7,V5 and V1 are changed so that valves V3 and V7 become closed and valvesV5 and V1 are opened. Waste gases received from the furnace through lineor ducting 36 are now directed into the top of the regenerator bed 34and drawn by fan 37 through regenerator bed 34 before being passed tothe chimney for discharge.

The operation of the valve as described ensures that there is always aflow of hot air to the reaction tower 26.

The static regenerator beds 34 and 35 may consist of refractory or metalballs of 19 mm diameter. The bed material which in this example consistsof the 19 mm balls can be discharged intermittently for cleaning, andreplaced by clean balls fed into the beds under gravity.

In operation of the apparatus of FIG. 3 in a method in which glass ismelted at 1440° C., waste gases at about 1300° C. are passed through theregenerator bed 34 or 35 which is in the waste gas receiving part of itscycle, and the relevant bed is heated near to this temperature. Duringthe succeeding air delivery part of the cycle of that regenerator bed,atmospheric air to be used for combustion is heated to a temperature ofthe order of 1200° C., a heat transfer from waste gases to combustionair in excess of 90% being achieved.

By the use of the apparatus of FIG. 3 in which the upper cylindricalsection 27 of reaction tower 26 allows time between the point where theglass batch is mixed with the heated combustion air introduced at 32 andthe point where fuel is added at the top of lower cylindrical section28, the glass is preheated at the expense of the heat contained in thecombustion air introduced at 32. In consequence the temperature of thecombustion air is reduced to a temperature below 700° C. before the fuelis added, and the quantity of NO_(x) which results from the introductionof the fuel and the consequent combustion is also reduced to the orderof 300 ppm of the waste gas as explained above with reference to FIG. 2.

I claim:
 1. A method of feeding glass batch to a glass-melting furnace,which includes the steps of:(a) feeding powdered glass batch verticallydownwardly through a hot air environment; (b) generating infra-sound;(c) directing the infra-sound towards the hot air environment containingthe powdered glass batch to facilitate a transfer of heat from the hotair environment to the powdered glass batch; and (d) subsequent to thesaid transfer of heat, adding fuel to the heated glass batch to heat theglass batch to a melting temperature.
 2. A method according to claim 1wherein the transfer of heat cools the hot air environment to atemperature below 700° C.
 3. A method according to claim 1 wherein thehot air environment is provided by an airstream pre-heated by wastegases from the glass-melting furnace.
 4. A method according to claim 3wherein the airstream is pre-heated to a temperature of at least 1,200°C.
 5. A method of feeding glass batch to a glass-melting furnacecomprising a crown, for making a vitreous material comprising the stepsof:(a) passing a heated airstream containing air at a temperature inexcess of 1,000° C. vertically downwardly towards the crown of theglass-melting furnace in which there is a molten glass upper surface;(b) introducing powdered glass batch into the heated airstream; (c)generating infra-sound; (d) directing the infra-sound towards the heatedairstream to vibrate the heated airstream and effect heat transfer fromthe heated airstream to the powdered glass batch to heat the powderedglass batch and cool the heated airstream to a temperature below 700° C.to provide a cooled airstream; (e) subsequently adding fuel as theheated powdered glass batch and the cooled airstream move downwardlytowards the crown of the furnace; and (f) passing a stream of powderedglass batch, burning fuel and air downwardly through the crown of thefurnace to provide a flame of the burning fuel such that there is directcontact between the flame of the burning fuel and the molten glass uppersurface within the furnace, and the glass batch is melted.
 6. A methodaccording to claim 5 wherein the fuel is added around a circumference ofthe heated airstream and heated glass batch particles.
 7. A methodaccording to any one of the preceding claims wherein the glass batchforms a glass having a melting point in excess of 1400° C.